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| <h2 title="Annotation Type DoFn.ProcessElement" class="title">Annotation Type DoFn.ProcessElement</h2> |
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| <pre>@Documented |
| @Retention(value=RUNTIME) |
| @Target(value=METHOD) |
| public static @interface <span class="memberNameLabel">DoFn.ProcessElement</span></pre> |
| <div class="block">Annotation for the method to use for processing elements. A subclass of <a href="../../../../../org/apache/beam/sdk/transforms/DoFn.html" title="class in org.apache.beam.sdk.transforms"><code>DoFn</code></a> must have |
| a method with this annotation. |
| |
| <p>The signature of this method must satisfy the following constraints: |
| |
| <ul> |
| <li>If one of its arguments is a <a href="../../../../../org/apache/beam/sdk/transforms/splittabledofn/RestrictionTracker.html" title="class in org.apache.beam.sdk.transforms.splittabledofn"><code>RestrictionTracker</code></a>, then it is a <a |
| href="https://s.apache.org/splittable-do-fn">splittable</a> <a href="../../../../../org/apache/beam/sdk/transforms/DoFn.html" title="class in org.apache.beam.sdk.transforms"><code>DoFn</code></a> subject to the |
| separate requirements described below. Items below are assuming this is not a splittable |
| <a href="../../../../../org/apache/beam/sdk/transforms/DoFn.html" title="class in org.apache.beam.sdk.transforms"><code>DoFn</code></a>. |
| <li>If one of its arguments is tagged with the <a href="../../../../../org/apache/beam/sdk/transforms/DoFn.Element.html" title="annotation in org.apache.beam.sdk.transforms"><code>DoFn.Element</code></a> annotation, then it will be |
| passed the current element being processed; the argument type must match the input type |
| of this DoFn. |
| <li>If one of its arguments is tagged with the <a href="../../../../../org/apache/beam/sdk/transforms/DoFn.Timestamp.html" title="annotation in org.apache.beam.sdk.transforms"><code>DoFn.Timestamp</code></a> annotation, then it will be |
| passed the timestamp of the current element being processed; the argument must be of type |
| <a href="https://static.javadoc.io/joda-time/joda-time/2.10.1/org/joda/time/Instant.html?is-external=true" title="class or interface in org.joda.time"><code>Instant</code></a>. |
| <li>If one of its arguments is a subtype of <a href="../../../../../org/apache/beam/sdk/transforms/windowing/BoundedWindow.html" title="class in org.apache.beam.sdk.transforms.windowing"><code>BoundedWindow</code></a>, then it will be passed the |
| window of the current element. When applied by <a href="../../../../../org/apache/beam/sdk/transforms/ParDo.html" title="class in org.apache.beam.sdk.transforms"><code>ParDo</code></a> the subtype of <a href="../../../../../org/apache/beam/sdk/transforms/windowing/BoundedWindow.html" title="class in org.apache.beam.sdk.transforms.windowing"><code>BoundedWindow</code></a> must match the type of windows on the input <a href="../../../../../org/apache/beam/sdk/values/PCollection.html" title="class in org.apache.beam.sdk.values"><code>PCollection</code></a>. If the |
| window is not accessed a runner may perform additional optimizations. |
| <li>If one of its arguments is of type <a href="../../../../../org/apache/beam/sdk/transforms/windowing/PaneInfo.html" title="class in org.apache.beam.sdk.transforms.windowing"><code>PaneInfo</code></a>, then it will be passed information |
| about the current triggering pane. |
| <li>If one of the parameters is of type <a href="../../../../../org/apache/beam/sdk/options/PipelineOptions.html" title="interface in org.apache.beam.sdk.options"><code>PipelineOptions</code></a>, then it will be passed the |
| options for the current pipeline. |
| <li>If one of the parameters is of type <a href="../../../../../org/apache/beam/sdk/transforms/DoFn.OutputReceiver.html" title="interface in org.apache.beam.sdk.transforms"><code>DoFn.OutputReceiver</code></a>, then it will be passed an |
| output receiver for outputting elements to the default output. |
| <li>If one of the parameters is of type <a href="../../../../../org/apache/beam/sdk/transforms/DoFn.MultiOutputReceiver.html" title="interface in org.apache.beam.sdk.transforms"><code>DoFn.MultiOutputReceiver</code></a>, then it will be passed |
| an output receiver for outputting to multiple tagged outputs. |
| <li>If one of the parameters is of type <a href="../../../../../org/apache/beam/sdk/transforms/DoFn.BundleFinalizer.html" title="interface in org.apache.beam.sdk.transforms"><code>DoFn.BundleFinalizer</code></a>, then it will be passed a |
| mechanism to register a callback that will be invoked after the runner successfully |
| commits the output of this bundle. See <a |
| href="https://s.apache.org/beam-finalizing-bundles">Apache Beam Portability API: How to |
| Finalize Bundles</a> for further details. |
| <li>It must return <code>void</code>. |
| </ul> |
| |
| <h2>Splittable DoFn's</h2> |
| |
| <p>A <a href="../../../../../org/apache/beam/sdk/transforms/DoFn.html" title="class in org.apache.beam.sdk.transforms"><code>DoFn</code></a> is <i>splittable</i> if its <a href="../../../../../org/apache/beam/sdk/transforms/DoFn.ProcessElement.html" title="annotation in org.apache.beam.sdk.transforms"><code>DoFn.ProcessElement</code></a> method has a parameter |
| whose type is of <a href="../../../../../org/apache/beam/sdk/transforms/splittabledofn/RestrictionTracker.html" title="class in org.apache.beam.sdk.transforms.splittabledofn"><code>RestrictionTracker</code></a>. This is an advanced feature and an overwhelming |
| majority of users will never need to write a splittable <a href="../../../../../org/apache/beam/sdk/transforms/DoFn.html" title="class in org.apache.beam.sdk.transforms"><code>DoFn</code></a>. |
| |
| <p>Not all runners support Splittable DoFn. See the <a |
| href="https://beam.apache.org/documentation/runners/capability-matrix/">capability matrix</a>. |
| |
| <p>See <a href="https://s.apache.org/splittable-do-fn">the proposal</a> for an overview of the |
| involved concepts (<i>splittable DoFn</i>, <i>restriction</i>, <i>restriction tracker</i>). |
| |
| <p>If a <a href="../../../../../org/apache/beam/sdk/transforms/DoFn.html" title="class in org.apache.beam.sdk.transforms"><code>DoFn</code></a> is splittable, the following constraints must be respected: |
| |
| <ul> |
| <li>It <i>must</i> define a <a href="../../../../../org/apache/beam/sdk/transforms/DoFn.GetInitialRestriction.html" title="annotation in org.apache.beam.sdk.transforms"><code>DoFn.GetInitialRestriction</code></a> method. |
| <li>It <i>may</i> define a <a href="../../../../../org/apache/beam/sdk/transforms/DoFn.GetSize.html" title="annotation in org.apache.beam.sdk.transforms"><code>DoFn.GetSize</code></a> method. |
| <li>It <i>may</i> define a <code>GetPartitition</code> method. |
| <li>It <i>may</i> define a <a href="../../../../../org/apache/beam/sdk/transforms/DoFn.SplitRestriction.html" title="annotation in org.apache.beam.sdk.transforms"><code>DoFn.SplitRestriction</code></a> method. |
| <li>It <i>may</i> define a <a href="../../../../../org/apache/beam/sdk/transforms/DoFn.NewTracker.html" title="annotation in org.apache.beam.sdk.transforms"><code>DoFn.NewTracker</code></a> method returning a subtype of <code>RestrictionTracker<R></code> where <code>R</code> is the restriction type returned by <a href="../../../../../org/apache/beam/sdk/transforms/DoFn.GetInitialRestriction.html" title="annotation in org.apache.beam.sdk.transforms"><code>DoFn.GetInitialRestriction</code></a>. This method is optional in case the restriction type returned by |
| <a href="../../../../../org/apache/beam/sdk/transforms/DoFn.GetInitialRestriction.html" title="annotation in org.apache.beam.sdk.transforms"><code>DoFn.GetInitialRestriction</code></a> implements <a href="../../../../../org/apache/beam/sdk/transforms/splittabledofn/HasDefaultTracker.html" title="interface in org.apache.beam.sdk.transforms.splittabledofn"><code>HasDefaultTracker</code></a>. |
| <li>It <i>may</i> define a <a href="../../../../../org/apache/beam/sdk/transforms/DoFn.GetRestrictionCoder.html" title="annotation in org.apache.beam.sdk.transforms"><code>DoFn.GetRestrictionCoder</code></a> method. |
| <li>The type of restrictions used by all of these methods must be the same. |
| <li>Its <a href="../../../../../org/apache/beam/sdk/transforms/DoFn.ProcessElement.html" title="annotation in org.apache.beam.sdk.transforms"><code>DoFn.ProcessElement</code></a> method <i>may</i> return a <a href="../../../../../org/apache/beam/sdk/transforms/DoFn.ProcessContinuation.html" title="class in org.apache.beam.sdk.transforms"><code>DoFn.ProcessContinuation</code></a> to |
| indicate whether there is more work to be done for the current element. |
| <li>Its <a href="../../../../../org/apache/beam/sdk/transforms/DoFn.ProcessElement.html" title="annotation in org.apache.beam.sdk.transforms"><code>DoFn.ProcessElement</code></a> method <i>must not</i> use any extra context parameters, such |
| as <a href="../../../../../org/apache/beam/sdk/transforms/windowing/BoundedWindow.html" title="class in org.apache.beam.sdk.transforms.windowing"><code>BoundedWindow</code></a>. |
| <li>The <a href="../../../../../org/apache/beam/sdk/transforms/DoFn.html" title="class in org.apache.beam.sdk.transforms"><code>DoFn</code></a> itself <i>may</i> be annotated with <a href="../../../../../org/apache/beam/sdk/transforms/DoFn.BoundedPerElement.html" title="annotation in org.apache.beam.sdk.transforms"><code>DoFn.BoundedPerElement</code></a> or <a href="../../../../../org/apache/beam/sdk/transforms/DoFn.UnboundedPerElement.html" title="annotation in org.apache.beam.sdk.transforms"><code>DoFn.UnboundedPerElement</code></a>, but not both at the same time. If it's not annotated with either of |
| these, it's assumed to be <a href="../../../../../org/apache/beam/sdk/transforms/DoFn.BoundedPerElement.html" title="annotation in org.apache.beam.sdk.transforms"><code>DoFn.BoundedPerElement</code></a> if its <a href="../../../../../org/apache/beam/sdk/transforms/DoFn.ProcessElement.html" title="annotation in org.apache.beam.sdk.transforms"><code>DoFn.ProcessElement</code></a> method |
| returns <code>void</code> and <a href="../../../../../org/apache/beam/sdk/transforms/DoFn.UnboundedPerElement.html" title="annotation in org.apache.beam.sdk.transforms"><code>DoFn.UnboundedPerElement</code></a> if it returns a <a href="../../../../../org/apache/beam/sdk/transforms/DoFn.ProcessContinuation.html" title="class in org.apache.beam.sdk.transforms"><code>DoFn.ProcessContinuation</code></a>. |
| </ul> |
| |
| <p>A non-splittable <a href="../../../../../org/apache/beam/sdk/transforms/DoFn.html" title="class in org.apache.beam.sdk.transforms"><code>DoFn</code></a> <i>must not</i> define any of these methods.</div> |
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